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Researchers studying bipolar disorder say the risky decisions people make during manic episodes come from deep inside their brains in a primal, pleasure-seeking region also linked to drug addiction.

Their findings, acquired using a game of roulette and a brain scanner, were published Tuesday in the journal BRAIN. "This study shows how we can use the new tools of neuroscience to better understand the psychological mechanisms that lead to a psychiatric disorder,” said co-author Richard Bentall of the University of Liverpool. Researchers from the University of Manchester also contributed to the study. Bipolar disorder, “until now, has been very difficult to understand."

But with functional magnetic resonance imaging, or fMRI, neuroscientists can watch the brain in action. It’s been used to spot the source of creativity among writers and the anguish that can lead to suicide. Here, they examined the brains of people with and without bipolar disorder as they gambled over a roulette table. What they discovered was not altogether unexpected.

Risky behavior is literally like crack for somebody who’s having a manic episode. A part of the brain called the nucleus accumbens, which operates on the flow of dopamine and serotonin, was more intensely active in participants with bipolar disorder than those without. (The same part of the brain is activated when rats are fed heroin and has been identified as a target for addiction treatments.)

An active nucleus accumbens alone isn’t a problem. It’s simply the source of desire — for drugs, sex, food — which we all have. What separates the healthy from the unhealthy is another part of the brain called the prefrontal cortex. Humans evolved this region much later to act as a regulator for destructive behavior, like the governor on your car forcing you to slow down. When faced with a risky roulette gamble, bipolar participants’ prefrontal cortexes weren’t telling them to think about their long-term strategy.

"The greater buzz that people with bipolar disorder get from reward is a double-edged sword,” said Wael El-Deredy, of the University of Manchester, in a statement. “On the one hand, it helps people strive towards their goals and ambitions, which may contribute to the success enjoyed by many people with this diagnosis. However, it comes at a cost: these same people may be swayed more by immediate rewards when making decisions and less by the long-term consequences of these actions."